R. S. Thomas

Davies, Damian Walford

doi:10.1093/obo/9780199846719-0058

Cited by 11 publications

(13 citation statements)

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“…While hydrogen was likely reionized at z > 6 (e.g., Fan et al 2006;Shull et al 2012a), quasars may have created sufficient photons with E > 4 ryd to reionize helium at z ∼ 3-4 (Furlanetto & Oh 2008). This is consistent with redshift estimates from the intergalactic medium (IGM) temperature (e.g., Becker et al 2011), which increases noticeably during helium reionization, as well as estimates from the redshift evolution of the He II Gunn-Peterson optical depth (e.g., Syphers et al 2011aSyphers et al , 2012Worseck et al 2011; but see Davies & Furlanetto 2012).…”

Section: Introductionsupporting

confidence: 77%

THE He II POST-REIONIZATION EPOCH:HST/COS OBSERVATIONS OF THE QUASAR HS1700+6416

Syphers

Shull

2013

ApJ

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The reionization epoch of singly ionized helium (He II) is believed to start at redshifts z ∼ 3.5-4 and be nearly complete by z ≃ 2.7. We explore the post-reionization epoch with far-ultraviolet spectra of the bright, high-redshift quasar HS1700+6416 taken by the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope, which show strong He II (λ303.78) absorption shortward of the QSO redshift, z QSO = 2.75. We discuss these data as they probe the post-reionization history of He II and the local ionization environment around the quasar and transverse to the line of sight. We compare previous spectra taken by the Far Ultraviolet Spectroscopic Explorer to the current COS data, which have a substantially higher signal-to-noise ratio. The Gunn-Peterson trough recovers at lower redshifts, with the effective optical depth falling from τ eff ≃ 1.8 at z ∼ 2.7 to τ eff ≃ 0.7 at z ∼ 2.3. We see an interesting excess of flux near the He II Lyα break, which could be quasar line emission, although likely not He II Lyα. We present spectra of four possible transverse-proximity quasars, although the UV hardness data are not of sufficient quality to say if their effects are seen along the HS1700 sightline.

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Section: Introductionsupporting

confidence: 77%

THE He II POST-REIONIZATION EPOCH:HST/COS OBSERVATIONS OF THE QUASAR HS1700+6416

Syphers

Shull

2013

ApJ

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“…To search for periodic variations in the long-term light curve, epoch-folding technique has been employed. This technique was described by Leahy et al (1983) and extended by Davies (1990Davies ( , 1991. It is less affected by harmonics, and more effective for nonsinusoidal modulations than the Fourier transform technique which is most sensitive to a periodic component of sinusoidal form in shape.…”

Section: Periodicity Analysismentioning

confidence: 99%

Optical quasi-periodic oscillation and color behavior of blazar PKS 2155–304

Zhang¹,

Zhao²,

Wang³

et al. 2014

Res. Astron. Astrophys.

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PKS 2155-304 is a well studied BL Lac object in the southern sky. The historical optical data during different period have been collected and compiled. Light curves with a time span of 35 years have been constructed. The R-band light curve has been analyzed by means of three methods: epoch folding method, Jurkevich method and discrete correlation function (DCF) method. It is derived that there is an evident periodic component of 317 days (i.e. 0.87 yr) superposed on a long-term trend with large-amplitude variation in the light curve. The variability of this source is accompanied by a slight color variation, and the brightness and color index are correlated with each other. On the long time-scale, PKS 2155-304 exhibits a tendency of bluer-when-brighter, which means the spectrum becomes flatter when the source brightens.

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“…Even prior to reionization the global approximation may be inadequate depending on the distribution of luminous sources. If exceedingly rare sources dominate ionization and heating, we would require a more detailed treatment (a problem recently addressed in the context of helium reionization by Davies & Furlanetto 2012).…”

Section: Caveatsmentioning

confidence: 99%

INTERPRETING THE GLOBAL 21 cm SIGNAL FROM HIGH REDSHIFTS. I. MODEL-INDEPENDENT CONSTRAINTS

Mirocha

Harker

Burns

2013

ApJ

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The sky-averaged (global) 21 cm signal is a powerful probe of the intergalactic medium (IGM) prior to the completion of reionization. However, so far it has been unclear whether it will provide more than crude estimates of when the universe's first stars and black holes formed, even in the best case scenario in which the signal is accurately extracted from the foregrounds. In contrast to previous work, which has focused on predicting the 21 cm signatures of the first luminous objects, we investigate an arbitrary realization of the signal and attempt to translate its features to the physical properties of the IGM. Within a simplified global framework, the 21 cm signal yields quantitative constraints on the Lyα background intensity, net heat deposition, ionized fraction, and their time derivatives without invoking models for the astrophysical sources themselves. The 21 cm absorption signal is most easily interpreted, setting strong limits on the heating rate density of the universe with a measurement of its redshift alone, independent of the ionization history or details of the Lyα background evolution. In a companion paper, we extend these results, focusing on the confidence with which one can infer source emissivities from IGM properties.

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R. S. Thomas

Cited by 11 publications

References 0 publications

THE He II POST-REIONIZATION EPOCH:HST/COS OBSERVATIONS OF THE QUASAR HS1700+6416

THE He II POST-REIONIZATION EPOCH:HST/COS OBSERVATIONS OF THE QUASAR HS1700+6416

Optical quasi-periodic oscillation and color behavior of blazar PKS 2155–304

INTERPRETING THE GLOBAL 21 cm SIGNAL FROM HIGH REDSHIFTS. I. MODEL-INDEPENDENT CONSTRAINTS

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